Stabilized interconnected sbr copolymer

ABSTRACT

AN UNVULCANIZED, INTERCONNECTED (LINEAR RUBBERY POLYMER) IS STABILIZED BY MEANS OF A BORATE OF A METAL SUCH AS MAGNESIUM, ZINC OR LEAD. IN THE RESULTING POLYMER, BUTADIENE-STYRENE COPOLYMER UNITS ARE INTERCONNECTED BY SILICON TETRACHLORIDE.

United States Patent Oflice US. Cl. 260--33.6AQ Claims ABSTRACT OF THEDISCLOSURE An unvulcanized, interconnected (linear rubbery polymer) isstabilized by means of a borate of a metal such as magnesium, zinc orlead. In the resulting polymer, butadiene-styrene copolymer units areinterconnected by silicon tetrachloride.

This invention relates to stabilizers for rubbery stereoregularhomopolymers of conjugated diolefins of 4 and 5 carbon atoms andcopolymers thereof with olefins, and more particularly the rubberycopolymer of butadiene and styrene, and especially the unvulcanized,oil-diluted interconnected (or jumped) polymers.

The term polymer is used herein to include homopolymers and copolymers.

The stabilizers of this invention are metal borates, and moreparticularly magnesium orthoborate, magnesium metaborate, leadmetaborate and zinc borate.

From 0.005 to 5 phr. (parts per hundred parts of the polymer), andgenerally from about 0.1 to 2 phr. will be used. Less may be used whenthe stabilizer of the invention is mixed with other stabilizer.

Unvulcanized interconnected rubbery polymers are those in which theviscosity and molecular weight have been jumped or otherwisesubstantially increased by reaction of the initially produced linearpolymer with a suitable reagent to increase the molecular weight and atthe same time the branching of the polymer. One type of such reaction isexemplified by the reaction of silicon tetrachloride with a livepolybutadiene produced by polymerization of butadiene in a non-aqueoussystem by means of a lithium-based catalyst (e.g., butyllithium ortetramethylene dilithium), the interconnected polymer containing asilicon atom in the center with four hydrocarbon polymer fragmentsextending therefrom to form a star. Another type of such interconnectingreaction, termed jumping, is exemplified by the procedure described byE. F. Engel et al., Rubber Age, December 1964, pages 410415; anyunsaturated rubbery polymer can be jumped by treatment with a two-partcatalyst consisting of a Friedel-Crafts catalyst plus a cocatalyst, suchas titanium tetrachloride and thionylchloride or ethylaluminumsesquichloride and water.

Another type of molecular-weight-increasing-reaction, or interconnecting(jumping) reaction, is exemplified by the reaction of an olefinicallyunsaturated rubbery polymer with a halogenated organic compound (e.g.ethylene dichloride) in the presence of a strong base (e.g.butyllithium) to produce a mixture of higher molecular weight rubberypolymers of branched construction, and, typically, exemplified by amixture of polymers having a molecular weight distribution including theoriginal molecular weight of the unreacted rubbery polymer to molecularweights of dimers, trimers, tetramers, and higher polymers of theoriginal rubbery polymer. All of these polymers of increased molecularweight contemplated by the invention have improved ability to acceptdiluting oil and possess good milling and extruding properties(processing properties) when extended with oil. From 3,591,548 PatentedJuly 6, 1971 to 100 parts of processing oil, or thereabout may be addedto 100 parts of the polymer.

Difficulty has been experienced in stabilizing many oil-diluted rubberypolymers. The stabilizer of this invention provides excellentstabilization of unvulcanized oil-diluted interconnected rubberypolymers, i.e. an unvulcanized linear rubbery polymer which has beeninterconnected and oil diluted. The invention finds widest use in thestabilization of such copolymers of butadiene and styrene but is usefulwith other interconnected rubbery polymers, and particularly thosederived from the polybutadienes, polyisoprenes and butadiene-isoprenecopolymers of any stereo composition. Polymers suitable for use in theinterconnecting reaction can be conveniently made by the methods of US.Pat. No. 3,317,918, for example.

Any of the oils commonly used in the dilution of rubbers can beemployed, including particularly higher boiling petroleum fractions suchas the commercially known naphthenic and aromatic mineral oils. In thedilution of rubbers with oils, about 37.5 parts of oil are customarilyused with 100 parts of polymer, although the amount of oil can vary from10 to 100 parts, more or less. The oil preferably is added to thepolymer after the polymerization and interconnecting reactions arecompleted. The stabilizer can be added prior to the addition of the oil,it can be added with the oil, or it can be added soon thereafter.

The stabilizer is incorporated into the polymer in the usual mannner.The stabilizing effect is recognized by the lessening of the decrease inthe viscosity of the polymer on heat aging. The stabilizers are added toprotect the polymer during storage and processing. The vulcanizates areuseful wherever rubber vulcanizates have been employed, as in themanufacture of tires, hose, and a wide variety of products.

The polymer used in the tests recorded in the following table wasprepared by reaction of SiCl With live butadienestyrene copolymerobtained through continuous nonaqueous polymerization utilizingbutyllithium as a catalyst. A polymer cement-oil masterbatch wasprepared containing 37.5 parts of processing oil per 100 parts ofpolymer, and the stabilizers of this invention were added to portions ofthe masterbatch to produce the samples for aging studies.

These masterbatch samples were desolventized on a drum drier. Each driedpolymer masterbatch sample was milled to achieve homogeneity and samplesof the appropriate size were cut from each of the milled polymers. AMooney viscosity (ml./4/212 F.) determination was made on each sampleprior to aging. Samples containing the various stabilizers were thenaged in a forced air oven at C. for various periods of time. The resultsobtained with the different stabilizers of this invention are recordedin the following table.

TAB LE Percent retention of Mooney viscosity (ml./4/212 F.

after aging) 2 4 6 Stabilizer days days days days ControL 96. 0 96. 093. 5 102. 5 No stabilizer 88. 5 83. 0 79. 0 75. 0 0.5 phr. magnesiumorthoborate 86. 5 84. 5 86. 5 93. 5 0.5 phr. magnesium metaborate 92. 587.0 89. 5 85. 0 0.5 phr. lead metaborate 92. 0 96. 0 96. 5 100. 0 0.5phr. zinc borate 96. 0 92. 0 90. 0 96. 0 0.5 phr. calcium metaborate 89.0 82. 0 78. 0 75. 5 0.5 phr. barium metaborate 86. 5 77. 5 79. 5 75. 00.5 phr. nickel borate 84. 5 79. 0 77. 0 75. 0

In the foregoing table, a sample containing no stabilizer is included aswell as a sample containing a commercial stabilizer and identified asControl. The barium, calcium carcass stocks. Also the stabilizedpolymers of the invention can be blended with other known polymers toprovide useful commercial compositions for fabrication into usefulshapes and articles. The stabilized polymers of the invention areadvantageously blended with known rubbers (e.g., natural rubber,polybutadienes, polyisoprenes, butadiene-styrene copolymer,isoprene-isobutylene copolymer, polychlorprene, isoprene-styrenecopolymer) with or without additional oils, for forming vulcanizates ofgreat technical importance. The novel stabilized polymers areadvantageously mixed with the known reinforcing carbon blacks to produceuseful commercial stocks, which also can contain one or more additionalrubbery polymers, and also can contain 5 to 100 phr. of additional oilor plasticizer. Sulfur and other known vulcanizing agents for naturalrubber and the commercial synthetic rubbers are useful for formingvulcanizable stocks containing the novel stabilized polymer. Knownmethods of mixing, forming, fabricating and curing or vulcanizingcompositions of natural and commercial synthetic rubbers are applicableto and useful with compositions containing the novel stabilized polymersof the 4 invention. The novel polymers are especially useful i pneumatictire tread, sidewall and carcass compositions, and the considerations ofthis paragraph are especially relevant to the use of the novel polymersin tires.

We claim:

1. Rubbery copolymer of butadiene and styrene copolymer units,interconnected by silicon tetrachloride, extended with 10 to parts ofprocessing oil per 100 parts of interconnected polymer, unvulcanized,and stabilized with 0.005 to 5 parts of a borate per 100 parts of thecopolymer, the borate being selected from the class consisting ofmagnesium orthoborate, magnesium metaborate, lead rnetaborate and zincborate.

2. The composition of claim 1 in which the stabilizer is magnesiumorthoborate.

3. The composition of claim 1 in which the stabilizer is magnesiummetaborate.

4. The composition of claim 1 in which the stabilizer is leadmetaborate.

5. The composition of claim 1 in which the stabilizer is zinc borate.

References Cited UNITED STATES PATENTS 2,935,485 5/1960 Reynolds260-23.7 3,281,383 10/l966 Zelinski et al. 260-23] DONALD E. CZAIA,Primary Examiner V. P. HOKE, Assistant Examiner US. Cl. X.R.

26023.7M, 23.7R, 45.7R, 45.75R

